Why Mosquitoes Love To Feast On Your Particular Blood

In recent years, we've been acculturated to think of vampires as svelte, sometimes sparkly biters of necks—or at least biters of Kristen Stewart. Mercifully, the closest most of us will get to a real life bloodsucker are the mosquitoes to whom we unwittingly donate 0.01 milliliters of our blood per bite.

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At best, you'll survive with an itchy nuisance. At worst, you can contract any of a number of debilitating viruses. This is one of the many reasons to avoid mosquitoes. But why are some people mosquito magnets more than others, and what can we do about it?

"This has been a topic of great research for decades," says Shannon Bennett, PhD, the associate curator of microbiology at San Francisco-based California Academy of Sciences. "We've either personally experienced or heard from others that 'oh, I'm so attractive to mosquitoes' or 'sweet-blooded' people abound. It's very hard to get really firm data on what's going on, so there's lots of theories out there and the support for them are all anecdotal."

Among the popular folk theories is that what we eat determines our attractiveness at the mosquito buffet. Not so, says Bennett, who specializes in the arboviruses spread by mosquitoes and other arthropods.

"We know that mosquitoes have evolved to hone in on the carbon dioxide that we exhale and signatures like body heat," says Bennett.

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Perhaps the biggest factor contributing to becoming a mosquito's meal is your scent—not just your body spray, but the microbes that live on your skin and the natural odors you produce that start with your genes.

Bennett points to a recent UK study, which used identical and fraternal twins to determine whether mosquitoes found certain subjects more attractive based on their individual smell.

"It was quite an elegant way of comparing two degrees of genetic relatedness, regular siblings and then identical twins which are going to be 100% genetically identical," says Bennett. "What was really cool is they put the mosquitoes in a chamber with two branches so that it looked like a Y—one branch going to a subject and the other branch either going to another subject or to clean air. They blew wind gently against the mosquitoes, and then observed whether the mosquitoes flew upwind towards one or the other source."

The researchers found that if the mosquitoes munched on one twin, it was more likely to munch on the other if they were identical.

"This suggests that people who are 100% genetically identical are more likely to show the same degree of attractiveness than people that are less identically related," says Bennett.

Now all scientists have to do is isolate what specific scents are attracting the mosquitoes. This is not an easy task given the complex way our genes are arrayed—there is no "odor" category so much as various genes in various places that each contribute to your own personal aroma.

"If we can identify what components of our genomes are encoding for that attractiveness, that will help us understand what specific scents they're attracted to."

Ultimately, the hope is that more effective repellents can be made, including personalized repellents for individuals based on their personal genome. Bennett suggests that someday we may take a pill that could turn on and off certain scent genes—including those that attract mosquitoes.

"It's just the beginning, but it's an exciting beginning, and if we can take it down to a specific genetic signatures, it could be the stuff of science fiction made real," says Bennett.

The incentive to pursue such a breakthrough is high given the type of viruses mosquitoes can carry. Aedes aegypti, for example, is a mosquito known to carry yellow fever, dengue fever and—wait for it—Chikungunya virus, which is sweeping through the Caribbean at present. (Read our full report on Chikungunya: The Agony Virus.)

Besides spraying yourself down with a mosquito-specific insect repellent—it's one of the 4 Best Ways to Repel Mosquitoes—another option is to prevent the bloodsuckers from breeding in the first place.

Mosquitoes breed by laying their eggs in standing water and, in warm weather, will mature from larvae (otherwise known as "wigglers") to full-blown disease carriers in about a week.

San Francisco's Department of Health advises people to look for and drain standing water around their homes. Also, look for hidden culprits like the saucers below flowerpots, hot tub covers, and roof gutters. By destroying these mosquito breeding grounds, you just might prevent your summer from biting the big one.

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